1. Field of the Invention
This invention relates to controlling video replay stores.
2. Description of the Prior Art
A video replay store controller is used in a video record/replay apparatus such as a digital video tape recorder (DVTR) to control the writing and reading of a replayed video signal to and from a multi-field replay buffer store. A previously proposed DVTR employing this arrangement is shown in the accompanying FIG. 1, in which blocks of replayed video data are supplied from a helical scanning tape transport mechanism 10, via a channel decoder 20, to a replay store 30.
The channel decoder provides synchronisation of the replayed data blocks, conversion from serial to parallel format, checking of identification data included in each data block, and a first level of error detection and correction.
The replay store 30 comprises four single-field stores, which are numbered 0 to 3 in FIG. 1. As each video field is replayed by the tape transport mechanism 10, it is stored in a field store selected by a store controller 40 according to a predetermined cyclic access sequence. Similarly, video fields for output by the DVTR are read out of a replay store selected by the store controller 40 according to the same cyclic access sequence. The multi-field replay store 30 is used as a buffer to allow asynchronously replayed video data to be processed and output by the DVTR at a constant and uniform field rate.
The store controller 40 relies on an indication of a transition between consecutively replayed video fields in order to select the correct stores for writing and reading the replayed video data. In a DVTR in which each video field is recorded as a plurality of blocks of video data, a field identifier can be included in each data block so that field transitions can be detected by checking for a change in the field identifiers of consecutively replayed data blocks.
It is known to provide DVTRs with multiple recording and replay heads. The provision of such multiple heads allows an increase in the overall data rate at which data can be written to or read from the storage medium.